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One of the key reasons to have raised beds is that they enable the soil to warm up to a temperature appropriate for germinating seeds and small plant starts. Separate them somewhat from the ground. To further improve things, I’m experimenting with a small greenhouse. I call it a "baby greenhouse".
The top is a simple frame with grooves to accommodate screen cord used to make/fix screen doors. The plastic is painters plastic. Works pretty well. The frame is assembled using using mortises and tenons. (I just got a mortising machine at the woodworking show this year)
Anyway, I have one of those wireless thermometers and using it, I think I have a winner. Whenever I check the temps inside and outside the cover, the difference is about 5 degrees F. Not bad. When things start to warm up, I think this will give me a lot of extra time in the growing season. If I’m just trying to avoid the last frost and I get 5 extra hit points (role playing games, anyone?) I could put stuff out a couple weeks early.
I’m thinking I’ll get some additional advantages as well. The soils in the beds is pretty drenched right now. Covering the beds should help. Cooler temps in the fall will be less of a hindrance as well.